Re: Revert: Remove useless self-joins *and* -DREALLOCATE_BITMAPSETS make server crash, regress test fail.

On Tue, May 7, 2024 at 8:29 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> David Rowley <dgrowleyml@gmail.com> writes:
> > Yeah, before the revert, that did:
> > -       sjinf->syn_lefthand = replace_relid(sjinf->syn_lefthand, relid, subst);
> > That replace code seems to have always done a bms_copy()
>
> Hmm, not always; see e0477837c.
>
> What I'm trying to figure out here is whether we have a live bug
> in this area in released branches; and if so, why we've not seen
> reports of that.

I didn't yet spot a particular bug.  But this place looks dangerous,
and it's very hard to prove there is no bug.  Even if there is no bug,
it seems very easy to unintentionally add a bug here.  Should we just
accept to always do bms_copy()?

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Regards,
Alexander Korotkov
Supabase